A typical multiple-gear bicycle includes a derailleur chain driven around one of a pair of front sprocket wheels and one of a plurality of rear sprocket wheels. The derailleur chain is composed of alternating outer pin links and inner roller links. To laterally move the derailleur chain between the front sprocket wheels and the rear sprocket wheels, the bicycle is provided with respective front and rear derailleurs. The front derailleur typically includes a pair of elongated parallel guide plates. The derailleur chain is disposed between the guide plates, and the chain moves in a direction generally orthogonal to the length of the guide plates.
The front derailleur contacts the derailleur chain in a couple situations. First, in response to certain gear changes by manipulation of gear control levers, the guide plates laterally shift so that one of the guide plates contacts the chain. When this contact reaches a predetermined threshold, the front derailleur causes the chain to "derail" from one front sprocket wheel and to move to the other front sprocket wheel. Second, if the gear control levers are not locked into a gear, but rather are set in-between two gears, the guide plates will be misaligned. This will likely cause one of the guide plates to "rub" against the moving chain. The effect of derailleur contact with the derailleur chain is better understood by knowledge of how the chain is constructed.
Existing derailleur chains are generally composed of alternating outer pin links and inner roller links. Each of the inner roller links includes a pair of inner parallel plates connected by a pair of parallel hollow cylinders surrounded by cylindrical rollers. Each of the inner parallel plates contains a pair of apertures coinciding with and communicating with the hollow ends of the cylinders. Each of the outer pin links includes a pair of outer parallel plates connected by a pair of parallel pins. One of the pins interconnects with a hollow cylinder in one adjacent inner roller link, while the other of the pins interconnects with a hollow cylinder in the other adjacent inner roller link. It is this interconnection of pins to hollow cylinders which forms a chain. The ends of the chain are terminated by inner roller links.
To form a single continuous chain as it appears on a bicycle (hereafter "bicycle chain"), the inner roller links at the ends of chain are connected to one another by either a conventional outer pin link or by what is commonly referred to as a master link. The master link is an outer pin link specially designed to permit disconnection and removal of the bicycle chain from the bicycle. As most bicycle users know, it is very difficult to remove a bicycle derailleur chain without a master link from a bicycle. A bicycle user typically removes the bicycle derailleur chain for cleaning and greasing. Such chain removal is especially common amongst mountain bike users, where the chain can collect much dirt while riding.
Existing master links employ several designs for permitting disassembly of master links. One type of master link, described in U.S. Pat. No. 5,178,585 to Lin et al. and produced by Ta Ya Chain Co., Ltd., includes a pair of parallel outer plates and a pair of parallel pins extending between the plates with the opposite ends or heads protruding from the surfaces of the respective plates. The pins are secured to one of the plates, and detachably engaged to respective "figure-eight" holes in the other plate. To disassembly this type of master link, the chain plate containing the "figure-eight" holes is pushed inward relative to the adjacent roller links so as to "pop off" the chain plate.
In another type of master link, produced by KMC Chain Industrial Co., Ltd. under the mark "MISSINGLINK".TM., the master link includes first and second parallel outer plates and a pair of parallel pins extending between the plates. One of the two pin heads on one of the pins is fixedly attached to the first plate and the other pin head is detachably engaged to a peanut-shaped aperture in the second plate. Similarly, one of the two pin heads on the other pin is fixedly attached to the second plate and the other pin head is detachably engaged to a peanut-shaped aperture in the first plate. The pin heads protrude from the surfaces of the respective plates. To disassemble the master link., the second pin heads are simultaneously disengaged from their respective apertures by moving the plates in opposite directions.
A drawback of both of these types of master links is that they are not designed for reuse following diassembly. If either type of master link is reused, it is weaker than its original form and it presents a safety hazard due to damage caused to either the plates or pins during reassembly. The master link become significantly weaker with every assembly and disassembly. The weakened master link is now a weak point in the bicycle chain which increases the risk of tooth "skipping" on the sprocket wheels or bicycle chain breakage during riding. Because of this damage to the master link, it is generally recommended that the master link be replaced with a new master link following disassembly. Thus, the master link is not reusable if a master link in optimum working condition is desired.
Another drawback of these types of master links is that the protrusion of the pin heads from the plate surfaces presents a risk that one of the derailleurs, especially the front derailleur, may "catch" on a pin head and cause the bicycle chain to jam on the front derailler. More specifically, since the front derailleur contacts the chain during gear changes or improperly set gears, one of the guide plates may catch on a master link pin head and jam the bicycle chain on the front derailler,
A further drawback of the chain link described in U.S. Pat. No. 5,178,585 to Lin et al. is that the lateral stress (side load) applied to the derailleur chain while riding may cause the master link to disassemble. This lateral stress results from the engagement of the derailleur chain with front and rear sprocket wheels which are not laterally aligned with one another, thereby causing the chain to flex. The possibility of accidental master link disassembly presents a safety hazard which should not be overlooked.
A need therefore exists to overcome the above-noted drawbacks associated with the foregoing types of master links.